The Medical College of Pennsylvania (MCP) and the Riverside Research Institute (RRI) will conduct a collaborative investigation of ultrasonic tissue characterization (UTC) features of thrombi. UTC features will be correlated with gross anatomic and microscopic properties and with clinical findings and outcomes. UTC methodology established at RRI will be developed further and applied to digitized rf echo signals from arterial and venous thrombi. RRI scattering theory will be refined and expanded for application to UTC of thrombi. Animal models will be developed and studies will be performed at MCP to evaluate the UTC features associated with thrombi having morphological features of red- cell fibrin mesh, dense fibrin-platelet regions, and loose fibrin mesh. These studies will be conducted in animals in vivo and studied over a time course to permit formulation of UTC features associated with type and age of thrombi. The results of the animal investigation will be applied in a clinical study of patients having lower-extremity, deep- vein thrombosis and carotid-artery thrombosis associated with atheromatous plaques. These clinical studies will help to establish UTC criteria for classification and staging of thrombosis and for monitoring treatment. A data base will be established and statistical analyses will be performed to correlate UTC features with microscopy and clinical findings, to develop discriminant functions for thrombus characterization, and to assess the clinical relevance of UTC.